There is great scientific and social interest in monitoring air pollutants indoors and outdoors. Many monitoring technologies for air pollutants have been developed and subsequently improved in the past few decades. Generally speaking, these technologies can be classified as either integrative collection or real-time analytical technologies. Both technologies can be further divided into two categories: active and passive methods.
Active methods directly pump air through collection or analytical devices to collect or analyze air pollutants. Therefore, electrical power is typically required. A passive (or diffusive) sampler is a device which is capable of taking samples of gas or vapor pollutants from air at a rate controlled by a physical process such as diffusion through a static air layer or permeation through a membrane and does not involve actively drawing or impelling the air through the sampler. Passive samplers are generally simple in structure and do not require electricity. Therefore, passive samplers are relatively cost-effective and convenient to use.
A number of different passive samplers have been developed and are in current commercial use. Passive sampling and systems for carrying out passive sampling are described, inter al, in the following documents:    Koutrakis, P.; Wolfson, J. M., Bunyaviroch, A., Froehlich, S. E., Hirono, K., and Mlik, J. D., (1993), “Measurement of ambient ozone using a nitrite coated filter”, Anal. Chem., 65, 209-214.    Krupa, S. and Legge, A., (2000), “Passive sampling of ambient, gaseous air pollutants: an assessment from an ecological perspective”, Environmental Pollution, 107, 31-45.    Lewis, R. G.; Mulik, J. D.; Coutant, R. W.; Wooten, G. W.; Mcmillin, C. R.; (1985), “Thermal desorbable passive sampling device for volatile organic chemicals in ambient air”, Analytical Chemistry, 57, 214-219.    3M, VOC passive sampler, www.3m.com    Ogawa & Company USA, http://ogawansa.com    Tang, H.; Brassard, B.; Brasssard R.; Peake, E.; (1997), “A New Passive Sampling System for Monitoring SO2 in the Atmosphere”, FACT, 1(5), 307-315.    Tang, H.; Lau, T.; Brassard B.; Cool, W., (1999), “A New All-season Passive Sampling System for Monitoring NO2 in Air”, FACT, 6, 338-345.    Tang, H. and Lau, L., (2000) “A new all season passive sampling system for monitoring ozone in air”, Environ. Monit. Assess. 65/1-2, 129-137.    Tang, H.; Sandeluk, J,; Lin L,; and Lown W.; (2002) “A new all season passive sampling system for monitoring H2S in air”, The ScientificWorld, 2, 155-168.    Uchiyama, S.; Asai, M.; Hasegawa, S.; (1999), “A scientific diffusion sampler for the determination of the volatile organic compounds in ambient air”, Atmospheric Environment, 33, 1913-1920.
All of the above-listed documents are hereby incorporated by reference for their teachings in connection with passive sampling systems. Of these, Krupa and Legge (2000) summarize the available passive samplers into different types, such as badge (3M), diffusion tube with filter absorption (Ogawa) or solid absorption (Uchiyama et al. 1999), and adsorption cartridge (Lewis et al. 1985) etc.
All of the passive samplers described in publications such as those identified above are used to collect a single air pollutant such as SO2, NO2, NOx, H2S, O3, NH3, VOC, ANK etc. As a practical matter, however, in many studies it is necessary to monitor several air pollutants in replication. Thus, a great number of passive samplers and rain shelters are needed at each location making for a cumbersome and expensive system and tedious set-up and collection operation.